The present invention relates to a method and apparatus for insulating the interior of a high temperature furnace and more particularly to an insulating mat or module for lining a furnace.
The problems involved in insulating the interior of a high temperature furnace are well known. Historically, the interiors of high temperature furnaces have been lined with various types of bricks capable of withstanding these high temperatures. When the brick lining wears out, however, it is an arduous and time-consuming task to replace the old brick with a new brick lining. On the other hand, efforts have been made to insulate the interior of a furnace with insulation which includes or consists of ceramic fiber material.
Refractory material, containing a high percentage of alumina and silica, has been produced in fibrous form and felted into blankets of various thickness and density. When used as an insulation layer, this alumina-silica material is characterized by good retardation of heat flow from the interior of furnaces to the outer surfaces of furnaces. Also, because of the very light density of the fibrous blanket, a furnace lined with such material stores a very small amount of heat in the furnace lining and thus permits rapid rates of heating and cooling with a concomitant of heat saving, especially when a process heating furnace is frequently cycled up and down in temperature.
Unfortunately, ceramic fiber blankets, which have heretofore been produced, are not mechanically strong. This material must be handled with great care to avoid tearing. Furthermore, the ceramic fiber blankets have differing values of mechanical strength depending upon the orientation of fibers with respect to the direction of applied forces, the relative amounts of alumina and silica and the heat treatment to which they have been exposed.
Ceramic fiber blankets are characterized by greater strength in a direction parallel to the surface of the blanket than transverse to these surfaces. Furthermore, because of the manner in which the ceramic fibers are felted to form blankets, the blankets are somewhat lamellar in structure and thus prone to easy separation in layers substantially parallel to the surfaces of the blanket. Thus, the ceramic fiber blanket material can be arranged in a manner as to take advantage of the superior strength in a direction substantially parallel to the surfaces of the blanket and in a manner to eliminate the peeling type deterioration of the blanket along lamellar plates.
Ceramic fiber blanket material is known to shrink when exposed to temperatures in excess of 2,000.degree. F. Previous methods for utilization of blankets of insulation fibers to the lining of furnaces have encountered difficulties caused by said shrinkage of the material. Separations or fissures transverse to the hot face of the furnace lining are often produced. Such fissures readily pass heat from the interior of the furnace towards the furnace shell resulting in unacceptable heat losses.
The prior art broadly discloses the feature of re-orienting fiber insulation, for examle U.S. Pat. No. 3,819,468 (Saunder et al) and U.S. Pat. No. 3,832,815 (Balaz et al), both show the cutting of strips of fibrous material from a sheet or blanket of ceramic fiber material, arranging the strips in side-by-side relation to provide an end fiber exposure in order to take advantage of the fiber's strength and insulative properties. However, furnace linings made in accordance with these teachings are composed of ceramic fibers which at elevated temperatures lack either the mechanical strength or the insulative properties or shrinkage resistance necessary to produce an enduring insulative product.
In accordance with the present invention, there is disclosed a furnace lining having a hot and cold face in the form of a mat or plurality of modules comprised of alternating strips of two fibrous materials. A first fibrous material is chosen for its shrinkage or corrosion resistance during high temperature use while the second fibrous material is chosen for its superior mechanical strength. The alternating strips of these two fibrous materials can be supported by an anchoring system or by veneering methods of cementing them to existing structures.
It is an object of this invention to provide a new and improved mat or insulative module lining which is composed of two fibrous materials having different properties yet exhibits the superior qualities of each type of fibrous material.
It is a further object of this invention to provide a furnace lining construction technique which increases the temperature use limit and the life of the fiber lining.